MICMAC / Get on Board (Microbes for Archaeological wood Conservation)

Interdisciplinary project aiming to develop a preventive and innovative extraction method to preserve waterlogged archaeological wood. This alternative method is based on sulfur oxidation and iron complexation to prevent salts efflorescence and wood acidification. This method does not alter the visual appearance or structure of the wood objects.

Thiobacillus denitrificans allows the oxidation of reduced sulfur species into sulfates.

Evaluation of the oxidation state of sulfur species present in a section of waterlogged wood contaminated with Fe²⁺ and S^2- ions (Sy-XRF imaging, Diamond Light Source, Oxford). Top: control sample. Bottom: sample after treatment with T. denitrificans. (pink: reduced sulfur species; blue: sulfates).

With the combination of T. denitrificans with siderophores (macromolecules complexing iron and naturally produced by microorganisms), a green extraction method is applied on waterlogged wood (oak and pine species), naturally or artificially contaminated with iron and sulfur.

Left: Raman spectra of waterlogged archaeological oak after chemical treatment (CT), biological treatment (BT) compared with untreated sample (NT). Right: Observations under stereomicroscope. M: mackinawite FeS, S: elemental sulfur α-S₈

The project aims currently to optimize extraction rates of iron and sulfur as well as to validate its compatibility with current consolidation methods of waterlogged archaeological wood (i.e. PEG– polyethylene glycol) and long-term efficiency through artificial ageing.

Collaborations :

• Haute Ecole Arc Conservation Restauration, HES-SO
• Archaeological service of Canton Bern
• Swiss national Museum
• Laboratoire Arc’Antique, Nantes, France
• Laboratoire des Sciences de l’Ingénieur pour l’Environnement (LaSIE), La Rochelle, France
• Mary Rose Trust, Portmouth, UK
• Haute Ecole d’Ingénierie et d’Architecture de Fribourg, HEIA-FR